If an attacker comes in with such force that you lose balance, you can turn the situation to your advantage using yoko-otoshi. Gripping the lapel of his gi, clothes or upper arm with the right hand and his punching arm with the left, drop back and to the right at an angle of 90° to the punch. Your weight and his momentum, together with a strategically placed leg to trip him should be enough to cause him to over-balance.
You can then encourage him on his way, by using your other leg to block his other leg and flick him over you.
Don’t forget to turn yourself with his momentum so that he has enough impetus to go over you.
Remember turning enough to the side
Remember you need a firm grip
Remember to flick the attacker’s leg
Remember to turn over